CN1791498A

CN1791498A - Making foamed bodies

Info

Publication number: CN1791498A
Application number: CNA2004800138181A
Authority: CN
Inventors: I·H·巴尔钦; M·A·J·费斯特; R·格兰姆斯
Original assignee: Stanelco RF Technologies Ltd
Current assignee: Stanelco RF Technologies Ltd
Priority date: 2003-05-20
Filing date: 2004-05-19
Publication date: 2006-06-21
Also published as: ATE350207T1; US20060279014A1; EP1631428B1; WO2004103687A8; GB0311494D0; CA2521434A1; JP2007502225A; DE602004004117D1; EP1631428A2; WO2004103687A1; AU2004240801A1; BRPI0410410A; DE602004004117T2

Abstract

Making foamed bodies by introducing a biodegradable polymer mixture into a mould (10) in which it is heated to form a foam and to fill the mould. The mould is defined between two opposed parts (12, 14) that mate together, and each mould part is of electrically conducting material, and the moulding surfaces are coated with an electrically insulating material (16). Radio-frequency signals are applied (25) between the mould parts (12, 14) so that the polymer mixture is heated by dielectric heating, so a foam tray is formed in less than 15 s. This provides a more rapid cycle time than using heated moulds. The radio frequency signals may be 27.12 MHz, or 40.68 MHz. The polymer may be starch-based.

Description

Make foams

The present invention relates to make the method and apparatus of foams, especially but not merely refer to those foams made from biodegradable or water miscible polymeric material.

In recent years, the exploitation of biodegradable condensate is devoted in considerable research, for example based on the condensate of starch.For example US 5 705 536 (Tomka) mentions: can be by powdered starch be mixed with water, and when water changes into steam extruding mixture, make starch foam.Tomka points out: it is favourable that the polymer mixture that uses thermoplastic starch or comprise thermoplastic starch is produced such foams; This starch comprises the water that is less than 1% weight usually, and Tomka has lectured: the fibrous material with for example comprising the lemon flaxen fiber of moisture, mix with starch.By in about 200 ℃ of extruding down, mixture can be changed into foam.By for example plasticizer and lubricant are added in the mixture, can change the characteristic of the product of generation.As explaining among US 6 235 815B (Loercks etc.), thermoplastic starch can be made by substantially anhydrous starch, in extrusion process, the plasticizer such as for example glycerine or sorbierite etc. of anhydrous starch and interpolation is stirred evenly, and melt anhydrous starch in the temperature range between 120 ℃ and 220 ℃; Thermoplastic starch can be in conjunction with the degradable condensate of other biological, as PCL.Loercks etc. have lectured: under drying condition, can make polymer mixture from directly having mixed for example hydrophobic polymeric anhydrous starch such as aliphatic polyester.US 6 494 704B (Andersen etc.) have described the molding press that is used for Production Example such as objects such as bowl or dish; these objects form between convex concave mould half one; and make by constituent based on starch; this constituent also comprises water and also can comprise fiber and inorganic filler, with between mold heated to 170 ℃ and 220 ℃.Mould can be metal for example steel or brass make, and can be furnished with the not adherent coating of PTFE.Some of the steam that permission generates are overflowed by ventilating opening, and other cause the foam expansion of material in the mould simultaneously.After the certain hour, preferably in the scope between 30 seconds and 2 minutes, can peel of mould half one, and remove foams.Be understood that be favourable heating cycle faster.

According to the present invention, a kind of method of making biodegradable foams is provided, the polymer mixture that wherein comprises biodegradable condensate and water is introduced in the mould, between the molded surface of two relative parts together that match each other, limit mould, wherein each mold component is made by conductive material, and each of molded surface is coated with electrical insulation material layer, wherein between mold component, apply radiofrequency signal, come heated polymerizable body mixture so that heat by dielectric, make water change steam into, thereby polymer mixture forms foam, fills mould, and is being no more than setting in 15 seconds.

Radio frequency source substantially can be between the frequency of 1MHz and 200MHz, usually between 10MHz and 100MHz, but implements strict restriction for any radio wave that sends.Therefore in practice, the selection of frequency may be more restricted.For example, source frequency can be 27.12MHz or 40.68MHz.This provides the more method of Fast Heating polymer mixture, so that heating, foaming and setting need be no more than 15 seconds, is preferably between 5 and 10 seconds.

The present invention also provides a kind of equipment of making foams with polymer mixture, this equipment is included in two and mates the mould that forms between the molded surface of relative parts together mutually, wherein each mold component is made by conductive material, and each of molded surface is coated with one deck electrically insulating material, and be included in the device that applies radiofrequency signal between the mold component, so that heat the polymer mixture that comes between the heating mould parts by dielectric.

The electrically insulating material that is used for applying molded surface is not preferably heated by dielectric, for example PFA (PFA).Silicone rubber also is suitable, provides good heat, electricity to install.The surface-coated of PTFE also is favourable, becomes easier because this makes foams be removed when in a single day formalizing.The thickness of electrical insulation material layer preferably is no more than 2mm.

Polymer mixture comprises water, and it forms steam when heating; Do not use other foaming agents.Polymer mixture is preferably based on the condensate of starch, and can comprise thermoplastic starch.In order to realize good foaming, when producing steam, it is crucial uprising at cavity pressure, makes steam can freely not discharge.

Only pass through example, and with reference to the accompanying drawings, will carry out further and description in more detail the present invention now, wherein:

Fig. 1 has shown when mold separation, through the cross sectional view of halves about the mould;

Fig. 2 has shown the view corresponding to Fig. 1 at mould inner foam body production period; And

Fig. 3 has shown the diagrammatic view of the circuit of the equipment that comprises mould.

With reference to Fig. 1 and 2, be used to produce equipment 10 by the made dish of the polymer material that bubbles based on starch, comprise mold halves 12 and 14 up and down respectively, last Lower Half is together paired with each other, thereby forms narrow cavity 15 betwixt, will form dish in cavity.Each mold halves 12 and 14 is made by brass, and each is in the coating 16 that has the PFA electrical insulator on the whole surface of cavity 15.When two and half ones 12 when 14 separate as shown in Figure 1, polymer material is introduced in the Lower Half 14, and the first half 12 is reduced to certain position subsequently.The peripheral ridge of being made by the electric insulation aluminium oxide 18 on the Lower Half 14 has the inner surface of inclination, and contact with the outward flange of respective shapes on the first half 12, make cavity 15 have the homogeneous thickness of 2.5mm, and half one 12 and 14 of mould accurately keep aiming at each other.Radiofrequency signal is applied between two and half ones 12 and 14 subsequently, and it plays the effect of electrode.Alumina ridge 18 guarantees that radiofrequency signal passes through cavity 15 and assemble.The polymer material heating, and the boiling of the water in the polymer mixture makes material become the foam of filling whole cavity 15.

Be close to peripheral ridge 18, upper mould half 12 defines peripheral grooves 20, and this peripheral grooves is communicated with mould cavity 15 through slit.Have some narrow ducts 22 (only having shown one of them among the figure), its from then on peripheral grooves 20 extend through upper mould half 12.Steam from the thermal polymer mixture can escape in the peripheral grooves 20, thereby overflows by narrow ducts 22, but carrier pipe 22 has limited flowing of steam, and when condensate bubbled, the pressure in the cavity 15 raise rapidly like this.Such as, this pressure can be elevated to 10 more than the atmospheric pressure.This reaches about temperature more than 185 ℃ corresponding to steam and polymer mixture.After about 8 seconds, polymer mixture forms the dish of self-supporting, and two and half ones separate once more, take out dish.

Be understood that by using the mould of suitable shape, can use this equipment to make the different product of wide range, and product can present the shape of any needs.For example, it can be used for making the multi-compartment dish, annulus or foursquare dish the bowl or cup or by two along the formed clamshell container of the hinged housing of linear edge.Only comprise single mould though the equipment that is understood that simultaneously is shown as, can be replaced by the mould that some formation are arranged, all these moulds are connected on the publicly-owned radio frequency source.

With reference now to Fig. 3,, diagram has shown circuit.As the radio-frequency signal generator 25 of solid condition apparatus, by coaxial cable 26 radiofrequency signal is fed on the matching network 28, from this network by coaxial cable 30 with signal provision on upper mould half 12, and bed die half 14 ground connection.Show matching network 28 in greater detail.Signal is delivered on the cable 30 by variable condenser 32, inductor 33 and variable condenser 34 etc.Supervisory circuit (not shown) monitoring radio-frequency current and voltage, and the numerical value of adjusting variable condenser 32 and 34 keep constant value, for example 50 ohm so that present to the impedance of generator 25.Contact between capacitor 32 and the inductor 34 is connected on the earth potential by capacitor 36, and effective capacitance that can regulating capacitor 36.This has played the effect that meticulous adjusting is applied to the radio-frequency current of radio-frequency voltage between charged electrode (upper mould half 12) and the relative earth electrode (bed die half one 14) and supply.Therefore it has controlled the power of actual provision between the mold halves 12 and 14.

Polymeric characteristic is not critical to the present invention, although condensate must be biodegradable, and preferably to small part based on starch.Condensate can comprise thermoplastic starch, but because this may not comprise a large amount of water, so in order to bubble, it is necessary comprising another composition that indispensable water is provided.Use a benefit of thermoplastic starch to be:, to be not easy water-soluble though the foams of generation are biodegradable.Select as another kind, condensate can comprise starch granules, and it is the gelatinize with the water reaction at least in part.Mixture can comprise salt (for example NaCl), changing its electric conductivity, and also can comprise plasticizer, for example sorbierite.Polymer mixture can comprise other polymer materials, and also can comprise reinforcing fiber, and for example those are from the cellulose organic fiber of hemp or cotton or other plant.Though fiber reinforcement the froth pulp that generates, it is about 50% that the content of fiber preferably is no more than, 25% of best no more than gross weight.Be understood that simultaneously polymer mixture can introduce in the mould with the form of film, particle, bead, rough machined finished product or paste mixture, and can be the appearance that wets.

For example, by quality such as cornstarch (corn flour) and water ground is mixed, thereby make the foamed starch dish.This mixture is introduced in the mould described above subsequently, and 2mm is thick, the cavity of 110mm diameter 15 but it has.When applying RF energy, starch mixture bubbles, and generates the foam dish of cavity filling.Volume increases greater than 3 times.

The equipment of being understood that can be changed by different way, and for example the thickness of the coating 16 of electrical insulator can be between 20 and 50 μ m.As mentioned above, mold shape depends on the shape of required product.When manufacturing comprises the product of hinge (for example clamshell container), can provide hinge by the bar (for example HYDROXY PROPYL METHYLCELLULOSE bar) of the non-foaming material of condensate, this is positioned at mould together with the mixture that forms foam, so that hinge strap and the foam segment on each side of hinge become an integral body.

Claims

1. method of making biodegradable foams, the polymer mixture that wherein will comprise biodegradable condensate and water is introduced in the mould, between the molded surface of two relative parts together that match each other, limit this mould, wherein, each mold component is made by conductive material, and each of molded surface is coated with one deck electrically insulating material, and wherein between mold component, apply radiofrequency signal, come heated polymerizable body mixture so that heat by dielectric, make water change steam into, so polymer mixture forms foam, fill mould, and be no more than setting in 15 seconds.

2. according to the method described in the claim 1, it is characterized in that, apply radiofrequency signal,, fill mould so that polymer mixture forms foam, and setting in less than 10 seconds.

3. according to the method described in claim 1 or 2, it is characterized in that, apply radiofrequency signal with the frequency between 20MHz and the 50MHz.

4. according to the method described in the claim 3, it is characterized in that, polymer mixture to small part based on starch.

5. each described method in requiring according to aforesaid right is characterized in that during bubbling process, the pressure in the mould is elevated to 10 more than the atmospheric pressure.

6. equipment of making foams from polymer mixture, this equipment is included in the mould that limits between the molded surface of two relative parts together that match each other, wherein, each mold component is made by conductive material, and be coated with one deck electrically insulating material, and be included in the device that applies radiofrequency signal between the mold component, so that heat polymer mixture between mold component by dielectric.

7. according to the equipment described in the claim 6, it is characterized in that the electrically insulating material that is used for applying molded surface is the material that is not heated by dielectric.

8. according to the equipment described in claim 6 or 7, it is characterized in that when mold component altogether the time, they separate by electrical insulator, the gap of electrical insulator proportional limit fixed mold is thick.